• Linxu的struct ifaddrs 与getifaddrs()函数


    来自man函数手册中的介绍:

    1,关于struct ifaddrs的说明:

    [cpp] view plaincopy
     
    1. struct ifaddrs  
    2. {  
    3.     struct ifaddrs  *ifa_next;    /* Next item in list */  
    4.     char            *ifa_name;    /* Name of interface */  
    5.     unsigned int     ifa_flags;   /* Flags from SIOCGIFFLAGS */  
    6.     struct sockaddr *ifa_addr;    /* Address of interface */  
    7.     struct sockaddr *ifa_netmask; /* Netmask of interface */  
    8.     union  
    9.     {  
    10.         struct sockaddr *ifu_broadaddr; /* Broadcast address of interface */  
    11.         struct sockaddr *ifu_dstaddr; /* Point-to-point destination address */  
    12.     } ifa_ifu;  
    13.     #define              ifa_broadaddr ifa_ifu.ifu_broadaddr  
    14.     #define              ifa_dstaddr   ifa_ifu.ifu_dstaddr  
    15.     void            *ifa_data;    /* Address-specific data */  
    16. };   


    2,关于getifaddrs()

    The getifaddrs() function creates a linked list of structures describing the network interfaces of the local system, and stores the address of the first
    item of the list in *ifap.  
    The list consists of ifaddrs structures, defined as follows:

           The ifa_next field contains a pointer to the next structure on the list, or
           NULL if this is the last item of the list.

           The ifa_name points to the null-terminated interface name.

           The ifa_flags field contains the interface flags

           The ifa_addr field points to a structure containing the interface address.

           The ifa_netmask field points to a structure containing the netmask associated with ifa_addr, if applicable for the address family.

           Depending on whether the bit IFF_BROADCAST or IFF_POINTOPOINT is set in ifa_flags (only one can be set at a time), either ifa_broadaddr will contain the broadcast address associated with ifa_addr (if applicable for the address family) or ifa_dstaddr will contain the destination address of the point-to-point interface.

           The ifa_data field points to a buffer containing address-family-specific data;this field may be NULL if there is no such data for this interface.

    返回值:
    On success, getifaddrs() returns zero; on error, -1 is returned, and errno is set appropriately.

    3,注意:
           The data returned by getifaddrs() is dynamically allocated and should be freed using freeifaddrs() when no longer needed.

    4,  man中的实例代码:

    [cpp] view plaincopy
     
      1. #include <arpa/inet.h>  
      2. #include <sys/socket.h>  
      3. #include <netdb.h>  
      4. #include <ifaddrs.h>  
      5. #include <stdio.h>  
      6. #include <stdlib.h>  
      7. #include <unistd.h>  
      8.   
      9. int main(int argc, char *argv[])  
      10. {  
      11.     struct ifaddrs *ifaddr, *ifa;  
      12.     int family, s;  
      13.     char host[NI_MAXHOST];  
      14.   
      15.     if (getifaddrs(&ifaddr) == -1) {  
      16.         perror("getifaddrs");  
      17.         exit(EXIT_FAILURE);  
      18.     }  
      19.   
      20.     /* Walk through linked list, maintaining head pointer so we 
      21.      *               can free list later */  
      22.   
      23.     for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {  
      24.         if (ifa->ifa_addr == NULL)  
      25.             continue;  
      26.   
      27.         family = ifa->ifa_addr->sa_family;  
      28.   
      29.         /* Display interface name and family (including symbolic 
      30.          *                   form of the latter for the common families) */  
      31.   
      32.         printf("%s  address family: %d%s ",  
      33.                 ifa->ifa_name, family,  
      34.                 (family == AF_PACKET) ? " (AF_PACKET)" :  
      35.                 (family == AF_INET) ?   " (AF_INET)" :  
      36.                 (family == AF_INET6) ?  " (AF_INET6)" : "");  
      37.   
      38.         /* For an AF_INET* interface address, display the address */  
      39.   
      40.         if (family == AF_INET || family == AF_INET6) {  
      41.             s = getnameinfo(ifa->ifa_addr,  
      42.                     (family == AF_INET) ? sizeof(struct sockaddr_in) :  
      43.                     sizeof(struct sockaddr_in6),  
      44.                     host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);  
      45.             if (s != 0) {  
      46.                 printf("getnameinfo() failed: %s ", gai_strerror(s));  
      47.                 exit(EXIT_FAILURE);  
      48.             }  
      49.             printf(" address: <%s> ", host);  
      50.         }  
      51.     }  
      52.   
      53.     freeifaddrs(ifaddr);  
      54.     exit(EXIT_SUCCESS);  
      55. }  
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  • 原文地址:https://www.cnblogs.com/myyan/p/4708050.html
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